@poptart:Well, the global biscuit community would have to disagree with your definition...
They are wrong and I spent ages looking at all the biscuit in Asda the other day and saw no Penguin bar type things.
British A small baked unleavened cake, typically crisp, flat, and sweet. - Oxford Dictionary
For a once great biscuit nation, there’s a depressing void of creativity here.
I think you will find there are still more types of classic biscuit available than in most countries. The Ginger Nut is still going strong and Bourbons are still available at 10p per metric tonne.
There is alot of experimentation but nothing sticks. I know this because at the end are all the discounted ideas McVities and the like have but no-one is buying. I took pity and sampled a vanilla, fudge and chocolate digestive. The fudge consistency far overpowered the fragile biscuit portion leaving a bendy gooey thing you had to chomp on as all the crumbs just clung to it and fell away.
In short. Generations of experimentation has settled on a pretty much optimal selection of biscuits in the shop isles.
I did try an Orea which Yanks go on about - biscuits were a bit dry, not brittle and filling was just sugar icing.
PS. The Digestive may be boring but each biscuit is the equivalent rda of fat and sugar for three weeks and was invented by the Victorians to keep explorers alive in arctic explorations.
PPS. If the Tim Tam is a Penguin and Penguin call it a biscuit in James Pond, the Tim Tam is thus ruled a biscuit.